1. Field of the Invention
The present invention relates to an outer dimension measuring apparatus and an outer dimension measuring method, and particularly relates to an outer dimension measuring apparatus and an outer dimension measuring method applied to measurement of an outer dimension of a thin wire member.
2. Description of Related Art
A laser scanning micrometer, an image sensor micrometer, an optical slicing two-dimensional shape measuring sensor, and the like are known examples of an apparatus conducting non-contact measurement of an outer dimension of a measured object such as a wire member.
For example, Japanese Patent Laid-open Publication No. 2011-106817 discloses a laser scanning micrometer. The laser scanning micrometer includes a light generator emitting a laser beam; a scanner scanning the laser beam over a measurement area; a photoreceiver receiving the laser beam passing through the measurement area; and a program calculating a dimension of a measured object based on a photoreception signal. In this example, a state where the scanning laser beam is blocked by the measured object is detected by the photoreceiver, an amount of time that the light is blocked is measured, the time is multiplied by speed, and the dimension of the measured object is calculated.
Japanese Patent No. 5507895 discloses an image sensor micrometer. The image sensor micrometer includes a projector emitting slit-shaped parallel light; a photoreceiver element receiving the slit-shaped parallel light passing through a dimension measurement area; a blocked light region detector detecting a blocked light region where light incident on the photoreceiver element is blocked by the measured object; and a dimension calculator calculating a dimension of the measured object based on the blocked light region. In this example, a size of a shadow cast by the measured object is detected by the photoreceiver element (an image sensor such as a CCD).
However, in the conventional outer dimension measuring apparatuses and outer dimension measuring methods, when the measured object is a thin wire member having an outer diameter of less than 10 μm, for example, measuring the outer dimension is difficult. Specifically, in the laser scanning micrometer, the wire member diameter is narrower than the diameter of the scanning laser beam, and only a portion of the laser beam is blocked by the measured object. Therefore, detecting the blocked light state is difficult. In addition, in the image sensor micrometer, detection of the blocked light region is difficult due to a reduction in contrast of the shadow due to diffraction (bending) of the light from the measured object, and due to limits on resolution determined by a pixel size of the image sensor.
The present invention provides an outer dimension measuring apparatus and an outer dimension measuring method capable of measuring an outer dimension of a measured object such as a thin wire member with a high degree of accuracy.